Method for making a pressureresponsive device



July 13, 1965 J. E. LINDBERG, JR 3,193,911

METHOD FOR MAKING A PRESSURE-RESPONSIVE DEVICE Filed July 12, 1962 ill'lv'iiir JOHN E. LINDBERG Jr.

INVENTOR.

BY 0,4, (MM. :M

United States Patent 3,193,911 NETHOD FOR MAKING A PRESSURE- RESPONEaIVE DEVICE John E. Lindberg, Jr., Alamo, Calif. (1211 Upper Happy Valley Road, Lafayette, Calif.) Filed July 12, 1962, Ser. No. 209,474 15 Claims. (Cl. 29-1555) This invention relates to a method for manufacturing a very sensitive pressure-responsive device having a snap action metal diaphragm. The invention is a continuationin-part of patent application Serial No. 86,252, filed January 26, 1961, which was a continuation-in-part of application Serial No. 815,406, filed May 25, 1959, now US. Patent No. 3,122,728, issued February 25, 1964.

In application Serial No. 815,406, I described and claimed a novel non-electric heat-detecting sensor connected to an electrical warning or corrective system by a novel pressure-actuated instrument that I term a responder, which formed the subject matter of application Serial No. 86,252. Combination of this responder with the sensor provides a completely hermetically sealed heatdetection transducer that is free from environmental errors that tend to be caused by pressure and altitude changes, moisture condensation, and so on. The responder itself is very sensitive, gives a snap action, is capable of great miniaturization, and is reliable under high-temperature conditions, in excess of 1000 F. It is substantially unaffected by ambient pressures or temperatures, is capable of withstanding rather high pressures without actuation and gives consistent results that are indefinitely repeatable for many, many cycles.

The obtaining of these characteristics leads to many manufacturing problems, some of which are solved by the present invention, whose general object is to provide an improved method for making the snap action diaphragm and the assembly thereof with the other elements of the responder.

It is an object of the invention to provide a method for providing a metal diaphragm with a generally spherical segment or blister, to provide snap action. A related object is to provide a method of forming such a blister that has uniform characteristics and that can be used over and over without wearing out and that can be used under very large pressure differentials and still provide snap action at a predetermined pressure.

Another object is to provide a method of maintaining the electrode tip against which the diaphragm moves so that it is always flush with the adjacent surface of the supporting structure, so that the diaphragm moves against a flat supporting structure and moves an exact distance, thereby giving both uniformity and insuring long life for the diaphragm.

A further object is to prevent internal corrosion of the parts after assembly and sealing.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment thereof.

In the drawings:

FIG. 1 is an enlarged view in perspective of a responder unit embodying the principles of the invention, the sensor attached thereto being broken off in order to conserve space.

FIG. 2 is a partially exploded view in perspective of the unit of FIG. 1.

3,193,911 Patented July 13, 1965 FIG. 3 is a further enlarged fragmentary view in elevation and in section of the unit of FIGS. 1 and 2 when initially assembled.

FIG. 4 is a view generally like FIG. 3 showing the device at the next stage in its manufacture.

FIG. 5 is a view like FIG. 3 showing the completed device in its unactuated position.

FIG. 6 is a view like FIG. 5 of the completed device in its actuated position.

A finished responder 10 made by the method of this in vention is shown in FIGS. 1, 5, and 6, while FIGS. 2, 3, and 4 show the responder 10 at certain stages of its manufacture. The finished responder 10 has a thin metal diaphragm 11 with a small spherical-segment active section 12, commonly called a blister (see FIG. 5). The diaphragm 11, the thickness of which has had to be greatly exaggerated in the drawings, is sandwiched between two body members 13 and 14 and divides the interior space into two chambers 15 and 16. When the pressure difference between the chambers 15 and 16 is nil or at least below a critical value, the diaphragm blister 12 is unactuated and remains as shown in FIG. 5. When the pressure difference reaches a critical value, the pressure in the champer 15 moves the blister 12 to its actuated position, shown in FIG. 6, where it remains until the pressure difference drops below its critical value. In its actuated position, the metal diaphragm 11 is in contact with the lower end 17 of an electrode 18, from which it was previously isolated. Thus, the diaphragm 11 and electrode 18 may be thought of as an electrical switch, closed by the pressure in the chamber 15 reaching a critical value.

It will be appreciated that uniformity of response both in any one responder 10 and in a plurality of supposedly identical responders 10 is very desirable. In order to obtain such uniformity and also reliability and long life, the method provided by the present invention is presented. It involves forming the blister 12 on the diaphragm 11 after assembly of the responder, and a number of other novel features.

The metal body member 13, preferably molybdenum, has a central recess 20 on its inside face, surrounded by an annular shelf 21. The edge 21a of the shelf 21 is rounded on a radius, is not sharp, as a protection to the diaphragm 11, so that movement of the diaphragm at that edge does not tend to cut the diaphragm. A central opening 22 leads through the member 13, and a tube 23, preferably Kovar, is brazed into the opening 22 to make a sub-assembly. Later, i.e., after assembly, a sensor 24 will be brazed into the tube 23. Then, the responder 10 will be actuated by the increase in pressure in the chamber 15 resulting from an increase in the temperature of the sensor 24.

Another sub-assembly is built upon the other body member 14, which is an annular disc, preferably molybdenum, fiat on both sides, including its inner surface 25, and is provided with a central opening 26, preferably of larger diameter than the opening 22 in the member 13 but of smaller diameter than the recess 20. A tube 27 of metal, preferably Kovar, is brazed into the opening 26 with its lower end flush with the surface 25. The interior of the tube 27 has a step 28 near its lower end, and a tube 30 of insulating material, preferably a high-temperature imporous ceramic, having a correspondingly stepped outer surface, is to be brazed into the tube 27 in the final braze, with its lower end also flush with the surface 25.

The electrode 18, preferably a molybdenum rod,also is installed so that its lower end 17 is flush with'the surface 25, so that the diaphragm 11 has on one side a substantially planar surface that supports it during actuat on except at amin-ute clearance 31 between the electrode '18 and the tube 30.

visible but gas will readily pass through it. The outel" end of theelectrode 18 (see FIG. 3) is drilled axially to I provide a stepped recess 32, into the upper end of which isbrazed a capillary tube 33, preferably of nickel. Pref.- erably, a small amount, of a metallic hydride getter 32a (e.g., palladium or titanium hydride) is inserted in the recess 32, for gettering remaining reactive gases after A; to the edge 21a of the shelf 21 or even opposite it on the plate 14; In factfthe whole lower surface of the diaphragm 11 may be'covered with stop-off. compound. The V, assemblyf the plate 13, brazingring 37, diaphragm 11,

This clearance 31 is barely, if at all,

} ring 38, and plate misaligned precisely and is then clamped securely and under considerable pressure, as by three molybdenum clamps disposed around the assembly,

and then the whole is'brazed under this pressure, preferably in a hydrogen furnace at approximately 2000 F.

completion of the devce and so preventing internal corrosion, etc. A passage 34- extends radially through the the chamber 16 by the clearance'31, and so that gas can be introduced'to .and withdrawn froni the chamber 16 by means of the capillary tube 33. A cap 35, preferably of Kovar, is to be brazed at the final braze to both of the tubes 30 and 33,1 and sealsthe chamber 16 except for the passage through the tube 33, suitable intermediary layers 'being used if desired 'or' needed for brazing the metal members to the ceramic ones.- The cap 35 seals the chamber 16 except for the passage through the tube 33,

audit will be noted that [the juncture of the cap 35 is spaced from the end of the'tube 30, the purpose of this being to provide a spacing sufficient so that the temperature coefficients of expansion are matched: that of the ceramic tube Stlbein-g matchedagainstthe'oombined ones of the electrode 18 and tube 33,'one of which expands more, and the other of which expands less, than does the tube 30 upon being heated, thereby maintaining the electrode tip'1'7 always flush :with the surface 25.

Before the final brazing, the second sub-assembly is put together substantially as follows: (1) the body member14 is pre-brazed to the Kovar tube 27, with the end of the tube-27 flush with-the surface (2) the rod 18 is drilled l5 rod 18 so that the interior of the tube33 is connected to f The rings 37 and 38 fuse intothe plates 13 and 14 and diaphragm 11, sealing them together, and they disappear as separatethicknesses, so that they are not shown in FIGS. 3 to 6, for any-increase in thickness is negligible. At the same time, the ube is brazed to the tube 27 and to the cap 35, .and the tube 33-;is brazed'to the cap 35.

The use of the stop-off compound is important because this means that after brazing the diaphragm 11 still has a little freedom to move between the plates 13 and 14- adjacent the inner edge 21a 'of the shoulder 21. Without 'a vacuum ror ine rt gas atmosphere, so that there is no "oxidation; otherwise the presence of oxygen makes little difference. The gas under pressure expands the metal 11 out in a spherical segment 41 shown in FIG. 4, which is somewhat beyond the, elastic limit of "the metal so that there is little recovery when the pressure is removed.

There is preferably a little over-forming at this stage.

After lowering the pressure in the chamber 16, then inert gasunder pressure is, put'into the chamber 15 on the opposite side of the diaphragm 11 'to force its segment to provide the, rccess'32, the tube 33 inserted and prcbrazed, the getter 32a being first put in, if used, and then the passage 34 is drilled; (3) the tube 30, prepared for.

brazing, is press fit into the tube 27; (4) the'rod 18 is inserted in the tube 30, :and the cap 35 put'on them both, the .rod end 1'7being adjusted to a flush: position and the top of the cap 35 swedged to the capillary tube '33, (5)

the end .17, surface 25, and lower ends of the tubes 27 and 30 are lapped and polished to insure fiushn ess and a good contact surface.

40 flat up against the elec'trode tip' 17, the tubes 27 and 30, and the surface 25. Much more pressure is used than is needed to flatten the segment-.40. This results in the Wrinkles 41 shown in FIGS. 5 and 6 and giving reliable,

foreseeable, repeatable, uniform results fromthen on.

7 There may be some cycling of the diaphragm 11 by alter- In some instances the electrode 18 has a tip dfdifferent material from the rest of the electrode; then, the procedure is basically the same, except for addition of the tip before the rod 18 is installed.

The diaphragm 11, which is preferably of molybdenum, 1 about 0.002" to 0.004" thick .and normally about /2" in diameter, has, in the meantime, received special heat treat In a vacuurn'furnace (e.g., one micron of mer-= ment. cury), it is heated to about 1850-1900 F. and preferably held the-re for about one hour, and then cooled, The

treatment results in removing stresses inherent in the metal and recrystallizes the metal structure, apparently forming larger crystals. This treatment provides a higher modulus of. elasticity, increases its strengthfmakes it more stable, "makes successive units more uniform, and eliminates criticalities in the brazing action that soon follows. This treatment of the diaphragm 11 is quite important;

With the first sub-assembly'ba'sed on thebody member now complete. absorb the various gases that might cause internal cornately increasing and decreasingthepressure in the chamber'15 to assure such uniformity. a

The responder 10, is now ready to be sealed. Leaving a desired pressure level of'argon or other'inert gas in the chamber, 16, the tube 33 is first closed and sealed. 1 The '7 chamber15 is then evacuated and the sensor 24 is brazed to thetube 23, and the chamber15 is sealed. Hydrogen is preferably introduced to the sensor 24 from its other end,';as explained in Serial No. 815,406, and a desired pressure of inert (e.g., noble) gas is provided there also. Then the sensor 24is sealed atlits other end, The unit is The getter 32a in the recess 32 acts to rosion; and the unit is very stable.

. To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention, The disclosures and the descrip- 13 and the second sub-assembly based on the body mem ber 14 both. completed, assembly of the responder 11) con- I tinues. The diaphragm 11, still'flat, is then sandwiched between the body members 13 and 14, sepa ated from compound (e.g.', chromium-oxide) 'isapplied-around their inner peripheries on the plates 13 and 14 and on the diaphragm 11, so that none of the braze metal canflow them by two very thin brazing rings 37 and 33. The rings v 37 .and' 38 are narrower than the shelf '21, and -stop-oif be-in any sense limiting.

tion hereinare purely illustrative and are not intended to' I claim: 1 1 v V 1. A method of providinga snap-action diaphragm from a thin flat sheet of metal comprising, holding a peripheral rim. portion only ofsaid sheet While first subjecting one side 'of the central portion bounded by said rim portion'to gas under pressure sufficient to stretch said 1 central portion beyond. its elastic limitand then relieving that pressure from that said side and applying gas under pressure totheother. side while backing up substantially the entire said central portion on said first side substantially on the plane of said rim portion, to provide a fold enabling repeatable recycling.

2. A method of making a snap-action diaphragm from a thin flat sheet of metal, comprising permanently securing a rim of said sheet to supporting metal members, leaving an unsupported area bounded by said rim, exerting sufficient gas pressure on one side of said area to permanently deform said area into a generally spherical segment, then relieving said pressure from said side, then exerting gas pressure on the opposite side of said area while backing up all of said area on a level with said rim, said pressure being in considerable excess of that required to flatten the central portion of said area, to provide a set of wrinkles so that action thenceforth of said diaphragm will be repeatable.

3. The method of claim 2 wherein after providing the set of wrinkles, the diaphragm is worked up and down by alternately applying and relieving the last named gas pressure, to improve the uniformity and reliability of diaphragm action.

4. A method of making a long-life snap-action diaphragm from a thin flat sheet of molybdenum, comprising pre-heat-treating said molybdenum by heating it under vacuum conditions at about 1900 F., cooling it, permanently securing a circumferential circular rim portion only of said sheet to supporting metal members, leaving an unsupported generally circular area, putting a noble gas under pressure on one side of said area to permanently deform said area into a generally spherical segment, and then relieving said pressure from said side.

5. The method of claim 4 followed by putting a noble gas under pressure on the opposite side of said area while backing up substantially the entire said area on a level with said rim portion, said pressure being in considerable excess of that required to flatten the central portion of said area, to provide a circular set of wrinkles so that action thenceforth of said diaphragm will be repeatable, and then alternately relieving and re-applying said lastnamed gas pressure to improve the repeatability, reliability, and uniformity of diaphragm action.

6. A method of making a pressure switch for use under severe temperature and pressure conditions, comprising the steps of:

securing and sealing a first tube to an opening in a first metal disc with one end of said tube flush with one side of said disc, said tube extending out beyond the other side thereof to an outer end,

securing an electrode in said tube with an end flush with said tube end, there being a very small clearance between said tube and said electrode,

brazing a thin metal diaphragm between said first disc and a raised rim portion of a second disc having a recess and a smaller opening with a second tube connected thereto,

forcing gas under pressure into said first tube via said clearance to said diaphragm to force the unbrazed portion of said diaphragm out beyond its elastic limit to form a spherical segment,

withdrawing said gas to lower said pressure,

forcing gas under pressure through said second tube into said recess to flatten said diaphragm against the firstnamed said disc and the ends of said first tube and said electrode, and

withdrawing said gas to lower said pressure, so as to condition said diaphragm for consistent repeatable action when gas is forced under pressure into said recess from said second tube and withdrawn therefrom.

7. The method of claim 6 wherein the brazing of said diaphragm is confined to an area outside the inner periphery of said rim portion, being spaced therefrom.

8. The method of claim 7 wherein the corner edge of said inner periphery is rounded to avoid sharp bending thereof.

9. A method of making a pressure switch for use under severe temperature and pressure conditions, comprising the steps of: r

securing and sealing a ceramic tube to a central open ing in a first metal disc, flush with one side of said disc and extending out beyond the other side thereof to an outer end,

securing a capillary tube to an opening in one end of an electrode that is solid except at said end, and there has a passage leading out radially from a terminal portion of said opening unfilled by said capillary tube.

securing and sealing a cap to said capillary tube and said ceramic tube to hold them together with said electrode flush with said one side of said disc, there being a very small clearance between said ceramic tube and said electrode,

brazing a thin metal diaphragm between said first disc and an outer rim portion of a second disc having a central recess and a smaller central opening with a tubular member connected thereto, forcing noble gas under pressure into said capillary tube and, via said radial passage and said clearance, to said diaphragm to force it out beyond its elastic limit to form a spherical segment and then lowering said pressure,

forcing noble gas under pressure through said tubular member into said recess to flatten said diaphragm against the first-named said disc and ceramic tube and electrode and then lowering said pressure.

10. The method of claim 9 wherein said rim portion is rounded to avoid a sharp edge and wherein stop-off compound is applied to both sides of said diaphragm before brazing, to cover an annular portion radially outside the inner periphery of said rim portion.

11. The method of claim 9 wherein the gas pressure is cyclically increased and decreased several times so as to make the response of the diaphragm uniformly reliable.

12. The method of claim 9 wherein the temperature coefficient of expansion of said ceramic tube lies between that of said electrode and said capillary tube and wherein the length of these three elements is related and said cap sealed to said capillary tube and said ceramic tube at a length assuring that the electrode end remains flush with said first metal disc at all times.

13. The method of claim 9 followed by placing noble gas into said clearance at a predetermined desired pressure and then sealing said capillary tube.

14. The method of claim 13 wherein a getter is placed into the space comprising the clearance and passage to take up remaining corrosive gases after sealing.

15. A method of making a pressure switch for use under severe temperature and pressure conditions, comprising the steps of: V

press-fitting a ceramic tube to a tubular central opening in a first metal disc, flush with one side of said disc and extending out beyond the other side thereof to an outer end, securing a capillary tube to an opening in one end of an electrode that is solid except at said end, and there has a passage leading out radially from a terminal portion of said opening unfilled by said capillary tube.

swedging a cap to said capillary tube and press-fitting said cap to said ceramic tube to hold them together with said electrode flush with said one side of said disc, there being a very small clearance between said ceramic tube and said electrode,

simultaneously brazing said ceramic tube to said tubular opening and to said cap and said cap' to said capillary tube while also brazing a thin metal diaphragm between said first disc and an outer rim portion of a second disc having a central recess and a smaller central opening with a tubular member connected thereto,

forcing gas under pressure into said capillary tube and, via said radial passage and said clearance, to said diaphragm to force it out beyond its elastic limit to form a spherical segment and then lowering said pressure, v V V forcing 'gasunder pressure through said tubular member into said recess to flatten said diaphragm'against :the first-named said disc and ceramic tube and elec-' trode and then lowering said pressure.

' 7 References Cited by the Examiner I UNITED STATES PATENTS I 7 1,091,763 3/14 Pierce 113-44 Flanagan V 29407 WHIT ORE A; WILTVZ, P i ar Examiner. H 'F. CAMPBELL,"Examine r 

1. A METHOD OF PROVIDING A SNAP-ACTION DIAPHRAGM FROM A THIN FLAT SHEET OF METAL COMPRISING, HOLDING A PERIPHERAL RIM PORTION ONLY OF SAID SHEET WHILE FIRST SUBJECTING ONE SIDE OF THE CENTRAL PORTION BOUNDED BY SAID RIM PORTION TO GAS UNDER PRESSURE SUFFICIENT TO STRETCH SAID CENTRAL PORTION BEYOND ITS ELASTIC LIMIT AND THEN RELIEVING THAT PRESSURE FROM THAT SAID SIDE AND APPLYING GAS UNDER PRESSURE TO THE OTHER SIDE WHILE BACKING UP SUBSTANTIALLY THE ENTIRE SAID CENTRAL PORTION ON SAID FIRST SIDE SUBSTANTIALLY ON THE PLANE OF SAID RIM PORTION, TO PROVIDE A FOLD ENABLING REPEATABLE RECYCLING. 